My Lords, I remind the House of my entry in the register of Lords' interests. I am honoured to follow the cogent and well argued speech of the noble and gallant Lord, Lord Craig of Radley. Much what he said I agree with, but in a qualified way. I pay tribute to the noble Lords, Lord Ramsbotham and Lord Hannay of Chiswick, for securing the debate and congratulate the noble Lord, Lord Ramsbotham, on introducing it with such an interesting and comprehensive speech. I associate myself fully with the tributes to the noble and gallant Lord, Lord Bramall. As I was listening to him, it reminded me of my time as the Secretary of State for Defence, when I was not nearly as happy sometimes to hear him speak in your Lordships' House as I have been today.

As we await the State of the Union address it is relevant to remind ourselves that some progress has been made since President Obama's speech in Prague in 2009. Arguably the new START treaty and the nuclear security summits are the high points of this progress. However, it is undoubtedly the case that the steam has gone out of this agenda, which we all espoused and cheered to the echo at the time of Prague, and we watch US/Russia relationships sour, for a number of reasons, with some worry.

Although global stockpiles of nuclear weapons are down dramatically since the end of the Cold War, today there are more nuclear-armed states and some of the weapons are in the hands of the most unstable regimes and regions in the world. Today Iran appears to be on track for a nuclear weapon, and it was announced yesterday that North Korea is planning a nuclear test. Pakistan is increasing the size of its nuclear arsenal and its plutonium production and appears to be pursuing smaller warheads for missiles aimed at India. Despite Fukushima, plans for expanded civil use of nuclear power remain. Widespread dispersal of enrichment technologies will make it more, not less, difficult to secure and control nuclear materials in the future.

Some say the dangers of the current environment and their uncertainties strengthen the case for our continued reliance on nuclear weapons. In the short term, I agree with them. I was partly responsible for the decision to renew the UK nuclear deterrent in 2006 and I still do not support the unilateral abandonment of an independent UK deterrent. However, this is not 2006 and relevant factors have changed even since then, as has their significance. It is becoming clear that deterrence as a cornerstone of our defence strategy is decreasingly effective and increasingly risky. As nuclear technologies spread, it will be more difficult, not easier, to prevent acts of nuclear terrorism. In 2006 I believed that our deterrent could play a role in deterring nuclear terrorism by threatening any state known to support it, but as the sources of material used for terrorism multiply, it will be more difficult to pinpoint the state responsible. If one cannot do that, one has no target for a credible threat of retaliation.

Cyber attacks are more commonplace today and they will grow both in number and in intensity. Attribution of the source is difficult, if not impossible. Where one cannot attribute an attack to a source, again one cannot deter with a threat of massive retaliation. That is not to say that nuclear weapons are irrelevant to all 21st century challenges, but it is to say that they offer less of an insurance policy against the challenges we will face in the future.

Further, I invite noble Lords to reflect on recent research into the climate change impacts of even a small nuclear exchange, let alone the effects of one between superpowers. Since 2006, new scientific research has revisited the nuclear winter theme. The research, employing more sophisticated climate models, stresses the devastating climate effects that would follow the use of nuclear weapons. A major use would be suicidal. It would so alter the climate and, as a consequence, our agriculture, that the attacker's population would starve to death, even without any nuclear retaliation. Even a smaller nuclear exchange, for example, between India and Pakistan would produce global temperatures colder than any experienced in the last millennium, with massive impacts on agriculture affecting up to 1 billion people, particularly in China and the United States, causing economic damage and huge political instability around the world.

If we want to be secure against nuclear and other threats, we have to think more creatively than our current reliance on deterrence implies. We have to shift the emphasis away from the threat of massive retaliation to prevention of nuclear catastrophe and resilience in the face of any attacks. On the nuclear side, we must plan for the unthinkable, but prevention is our main route to safety. Fewer nuclear weapons and materials in the world must be better than more of both. Those who argue the opposite are dangerously overconfident about our ability to keep control of nuclear weapons and materials, particularly in the face of terrorists' ambitions. Prevention means a number of things. First, we have to get and keep better control of the world's nuclear weapons and materials. It is essential that the nuclear security summit in the Netherlands is ambitious. This is an issue for continued leadership attention. It is important that world leaders reaffirm their commitment to continue this process, and talk of the meeting in the Netherlands being the last of the series is foolish.

Secondly, we have to cap the problem by making progress towards a fissile material cut-off treaty. The issue of such a treaty cannot be allowed to languish in the conference on disarmament any longer; it has been there for far too long. Thirdly, it is essential that President Obama and President Putin meet and pursue a follow-on deal to the new START treaty as soon as possible. The US needs to show flexibility on missile defence, agreeing to share more details because that is the key to unlocking the door to further nuclear reductions and a deal in which the US could agree to reduce the warheads it holds in reserve and Russia could agree to cuts and more transparency about its non-strategic nuclear weapons. Fourthly, we must never miss an opportunity to tell both the US and China that they have a solemn international responsibility to ratify the Comprehensive Nuclear Test-Ban Treaty.

Fifthly, we have to work harder to strengthen the grand bargain at the heart of the non-proliferation treaty or risk losing it. We are becoming dangerously complacent about it. All states have a responsibility here, but the nuclear weapons states bear a special responsibility. Successive Governments have reduced the number of warheads in the UK arsenal, but we need to do more. Formally, we are committed to the like-for-like renewal of Trident and the operational posture of continuous at-sea deterrence. The Government and all Members of this House need to reflect further on this position. Are we telling the countries of the rest of the world that we cannot feel secure without nuclear weapons on continuous at-sea deployment while at the same time telling the vast majority of them that they must forgo indefinitely any nuclear option for their own security? Is that really our policy? If so, do we expect the double standard that it implies and indeed contains, to stick in a world of rising powers?

The non-nuclear weapon states signatories to the NPT committed themselves to non-nuclear status only in the face of a commitment by the nuclear weapon states to pursue disarmament. Some of that disarmament must come through multilateral negotiation and agreement, but some of it can come through independent action, as in the case of several rounds of announced reductions in the size of the UK nuclear warhead stockpile, none of which we negotiated with anyone else. The time is now right, in my view, to change our posture and to step down from continuous at-sea deterrence. This would demonstrate that nuclear weapons are playing less and less of a role in our national security strategy, and along with the reductions in stockpile numbers we have made, it would strengthen our ability to argue internationally for the kinds of measures I have outlined in this speech.

There are those, I know, who will argue that we have already done enough, that it is time for others to act and that, in any case, such measures will have no impact on the actions of the Irans and North Koreas of this world. They may well be right. Certainly, some states must be confronted with firm international action and other states must also step up and take their responsibilities more seriously if we are to avoid the worst. If a disastrous nuclear incident does occur, it will not be all or even partially the fault of this country, but what consolation will there be in the blame game the morning after London has been devastated by a terrorist nuclear attack? What consolation will there be when we cannot secure incontrovertible evidence of the source of the attack and therefore cannot use the nuclear weapons we have on continuous deployment, even should we wish to? What will the value of our insurance policy be then? Where will the consolation be if even a small nuclear exchange between India and Pakistan has the kind of climatic effect I described earlier? The choice is not between one risky and one risk-free future. There are no risk-free futures on offer.

The primary purpose of our policy must be to ensure that we never suffer the consequences of a nuclear attack. At this stage in our history, nuclear deterrence still has a residual role to play in achieving this objective, but the character of 21st century threats means that its shelf life is eroding. To achieve our objective, we now need to shift the emphasis to the kinds of measures I have talked about-on to reducing the chances of any nuclear weapon ever being used anywhere. That means the relentless pursuit of nuclear weapons reductions, a relentless strengthening of nuclear security and non-proliferation regimes, and a decreased reliance on nuclear weapons for national security by all, including ourselves.